Alternating-current motor



No. 620,965. I I Patented Mar. l4, I899. E. W. RICE, In. &. C. P. STEINMETZ.

ALTERNATING CURRENT MOTOR.

(Application filed July 29, 1893.] (No Model.) 4 Sheets-Sheet I.

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No. 620,965. Patented Mar. l4, I899. E. W. RICE, .IR. 81. C. P. STEINMETZ. ALTERNATING CURRENT MOTOR.

(Application filed July 29, 1893.) (No Model.) 4 Sheets-$heet 2.

No. 620,965. Patented Mar. l4, I899.

JR. &. C. P. STEINMETZ.

E.'W. RICE,

ALTERNATING CURRENT MOTOR.

(Application filed July 29, 1898.) (No Modal.) .4 Sheets$heet 3v No. 620,965. Patented Mar. I4, I899. E. W. RICE, 1n. &. C P. STEINMETZ.

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EDWIN \V. RICE, JR., OF SWAMPSCOTT, AND CHARLES P. STEINMETZ, OF-

LYNN, MASSACHUSETTS, ASSIGNORS TO THE GENERAL ELECTRIC COM- PANY, OF NEIV YORK.

ALTERNATlNG-CURRENT MOTOR.

SPECIFICATION forming part of Letters Patent No. 620,965, dated March 14, 1899.

Application filed July 29, 1893. Serial No. 481,907. (No model.)

' rent motors, particularly to that class adapted to be operated by single-phase alternating currents; and it embodies certain improvements enabling such motors to be started from rest under load with a large torque.

Our invention also comprises arrangements for modifying the character of the motor or altering the relations of its parts so that when a speed approaching the normal has been attained the motor may, if desired, be thereafter operated as a single-phase alternating motor of the induction type. To this end we arrange a field-magnet coil or an inducingcoil, which may or may not be wound on the moving member, and in inductive relation thereto, at such an angle as to produce a rotary effect, we provide a second coil, which we may close on itself by means of a switch, inserting, preferably, an adjustable resistance, or which we may supply with the primary currents, as hereinafter explained. We prefer to leave a third portion of the circumference of the inducing member without any winding or to provide it with a winding which is open-circuited while the motor is starting. As far as the starting action is concerned we regard these two arrangements as practically equivalent. \Vithin the field of the coils thus arranged we provide an induced member, preferably a closed-circuited winding on a revolvin g armature, although, as above indicated, either theind ucing or the induced member may be the revolving part.

Although we have spoken in this statement of invention of a coil in the singular, it is to be understood that we may adapt our invention to a multipolar arrangement, and such an arrangement we ordinarily prefer for various reasons, and we particularly prefer to use a magnetic structure with projecting teeth having recesses for the coils. On such a structure we place two windings spaced as if they were to form two of the windings of a three-phase motor, one of said windings being fed from the inducing-circuit and one being short-circuited. It will be seen that this arrangement will leave a third portion of the field-core unwound. This portion we may wind with a third coil or series of coils; but in this case, as stated above, the third coil or series of coils should be open-circuited while the motor is started.

In the accompanying drawings, which show various embodiments of our invention, Figures 1, 2, and 3 are explanatory diagrams. Figs. 4 and 5 are views, partly diagrammatic, of a multipolar motor arranged according to our invention. Fig. 6 is a'diagram of an armature-winding which we may employ, having resistances. Fig. 7 shows our improved motor in a different form, and Fig. 8 is an additional explanatory diagram.

In Fig. 1, which is inserted simply to explain the principles of our invention, A, B, and C are field or inducing coils arranged at an angle of one hundred and twenty degrees from each other around a short-circuited armature D. R is a variable resistance in the circuit of the coil 0. B is the primary coil and is fed from the single-phase mains. Coil A is short-circuited.

Suppose that the resistance R is cut out that is to say, that the coil C is short-circuited and that current is admitted to B. The coil B will set up lines of force which will induce secondary currents in both the armature D and the coils A and C. The secondary currents in D will also induce currents in both A and C. The result will be that the currents in D will lag behind the currents in B and that the currents in A and in C will lag by a diiterent and usually by a greater angle; but owing to the symmetry of the-system there will be no torque or the torque in one direction will be equal to that in the other. If,

now, the resistance R be adjusted to some considerable value,the motor will tend to start. The reason for this we understand to be that the currents in C, owing to the action of the resistance, will lag behind the impressed electromotive force less than do the currents in A, so that we have what may in general be regarded as an unsymmetrical three-phase system. \Ve lind that the resulting torque is a maximum when the resistance R becomes infil1lt6ll1 other words, when the coil C is open-circuited or removed altogether. This results in the form shown in Fig. 2, which is a simple elementary diagram of the motor shown in Figs. t and 5. Y The mains are connected to the extremities of the coils A and B, and a switch F is arranged which acts to short-circuit A on itself when desired. This switch F acts also to cut in a variable resistance.

If current be supplied to the motor and the switch F be closed, the machine will start under load. We understand the action to be somewhat as follows: The current in B induces a field of force, which induces secondary currents in D and in A lagging behind the primary currents. D also induces in A tertiary currents lagging still further. If, now, the resistance controlled by the switch F is actually zero, the current flowing in A will be the resultant of the two currents induced in it by B and D, and the phase of this resultant will depend on the character of D and of the magnetic circuits, as well as on its own self-induction, the. Suppose that the armature D is of very high resistance and few turns, so that its inducing power is small. Then the current in A will be practically due to.

the action of B only and will have the usual transformer lag, which may be perhaps one hundred and fifty degrees behind the current and one hundred and twenty degrees behind the magnetism of B. The motor will thus start and run left-handedly. If, on the other hand, as we prefer should be the case, D is so constructed as to have a high inducing power, there will be three magnetomotive forces acting to produce rotation instead of two, as in the case where the inducing power of the armature is small. The motor will start and run right-handedly. The phase relations of currents and magnetomotive forces in this case, where the inducing power of the armature is high, may be more clearly explained by reference to the diagram Fig. 8 of the drawings. In this diagram the line represents in magnitude and phase the primary current in the inducing member B of the motor, while the line D represents the current induced thereby in the closed-circuited winding on the armature or induced member D of the motor. The resultant 4t represents in magnitude and phase the resultant magnetomotive force due to the action of the primary current and the current in the induced member. In addition to these currents there is a'third current, which is generated in the accelerating or closed-circuited coil A on the primary member. This tertiary current is due to the combined action of the currents in B and D and lags in phase behind their resultant by an angle equal to nearly one hundred and eighty degrees, and therefore behind the current in the primary coil 13 by an angle greater than one hundred and eighty degrees, which is equivalent to a lead. This tertiary current lags behind the resultant & in the same manner that the secondary current D lags behind its inducing-current B. The tertiary current may therefore be represented by the vector A and lags something over ninety degrees behind the magnetomotive force 5,whieh is the resultant, as will be seen, of the tertiary current A and the resultant l, which latter, as previously stated, is the resultant of the original primary current B" and the current D in the induced member.

It will of course be understood that the phase relations and magnitudes shown in the diagram referred to illustrate the conditions existing in the case of one particular design of motor, and it will further be understood .that these magnitudes and phase relations vary with different designs of motor and that even for the same design of motor the values vary with different values of load. The diagram is not to be taken as illustrating a fixed and unalterable condition of affairs, butis to be considered as indicating one relation only of the large number which may exist between the currents and magnetomotive forces act ing in motors constructed in accordance with our invention. It will be seen that this starting effect depends 011 the fact that A is set at an angle to 13, for if it were parallel to it or one-half of the polar pitch from it there would be no shifting or rotary field and no torque.

The resistance controlled by the switch F serves to vary the volume and lag of the current in A and to control the starting torque. \Vhen this resistance becomes fairly large, a considerable portion of the primary current will flow through A instead of [lowing through the short circuit, as before, which serves to still further adjust and control the phase of the magnetism induced by A.

\Vhen the motor attains a speed which will vary with the particular machine and with the load, but which should preferalfly be nearly equal to that 'of synchronism, the switch F may be opened altogether. The action will then be that of a simple single-phase induction-motor, which, as is well known, will run in either direction with good elliciency if it is once started.

In Fig. 3 we have shown the connections of another form. In this case the coil 0 is not omitted, but is open-circuited by a switch F during the starting and is closed on itself at about the time when the switch F is opened. It then tends to add to the torque of the machine by keeping the currents of the armature D more nearlyin phase with the electromotive force, the action being the usual action of a short-circuited secondary.

Referring now to Figs. i and 5, which show our improved motor in a more practical form,

A A are one set of field-magnet coils, and B B are another set. These two windings or sets of coils correspond to the coils A and B of Fi 2 and are wound at an angle to each other; but as in this form the motor has four polar lines the angle is thirty degrees instead of one hundred and twenty degrees. These two coils each fill one-third of the circumference of the inducing member, the remaining portion being unwound in order to produce the unsymmetrical relation necessary for starting torque.

As shown more clearly in Fig. 5, each winding consists of four coils A A A A and B B B E the coils of each set being ninety degrees from each other and the two sets being displaced by thirty degrees. All of the coils are connected in series, 1 being the entrance-point, 2 the common point of the two windings, and 3 the exit-terminal. For convenience of comparison the same numbers are inserted at the corresponding points in Fig. 2. The current enters at the point marked 1, passes to the point a, thence around the coil B, thence out at b, thence to the point a, thence around the coil B, thence out at Z), thence to a around the coil B out at point b to a around the coil B and out at b to the point 2. A similar cycle starting from point 2 and ending at point 3 is repeated with the coils A A A A The switch F serves to short-circuit the coils A A A A during the period of starting with or without resistance. Dis the armature, shown in this case as the rotor, though it will be evident, as stated.

above, thateither member may rotate. The preferred form is shown in diagram in Fig. 6, and consists of several circuits, which may be short-circuited upon themselves when a speed approaching synchronisin is attained, but which in starting have resistances R R R in circuit, so as to reduce the lag of the armature-currents and to prevent them from attaining excessive values. The action of this motor is the'same as that of the elementary form shown in Fig. 2. In starting the switch F is adjusted in such a manner that the phase and volume of the current in A are such as to give a maximum torque, which is in general attained by cutting in a portion of the resistance. It will be seen that by the use of a resistance in this manner a portion of the primary current passes through the coil A,

resistance is of course selected which will give the desired difference of phase in any case. It is also evident that any number of fieldmagnet coils may be used in series, and sevally by short-circuiting or through resistances, so as to give a gradual and progressive difference of phase between adjacent sets of field-magnet coils. It is also possible to run a motor constructed in accordance with our invention without the use of a switch F, and such an applicationwe aim to embrace in our claims; but ordinarily the commercial efiicien cy of such a motor would be very much below that of one operated in the manner already described. In such a construction the inducing-coils would be connected in series, as shown; but part of them would be permanently shortcircuited by a permanent electrical connection used in place of the switch F. In fact, the switch F may be said to illustrate such a construction when it is kept permanently closed.

Fig. 7 shows the practical embodiment of the form illustrated in Fig. 3 and need not be further explained. lVith the three sets of coils, Figs. 3 and 7, it is also possible to substitute, each for each, the coils A O and their functions, and in this way the direction of rotation of the motor is readily reversedthat is, at the start the coil 0 can be closedcircuited, as described, and the coil A left open-circuited until speed is attained, when B and C may be thrown in circuit with each other, as described, and A may be short-circuited to suppress the lag of the armaturecurrents.

WVe have shown and described in this application two different species of motors i11- volving our inventions, represented, respectively, in Figs. 4 and 7. We intend to include in this case such generic claims as cover both forms and also certain claims directed more specifically to the form shown in Fig. 4c, reserving for our divisional application, Serial No. 655,485, filed October 16, 1897, such claims as relate more particularly to the form shown in Fig. 7.

e have used in this application the expression polar pitch. By that expression we mean to signify the angular distance at any particular instant, from one north pole to the next north pole in the same phase-for example, in a two-pole motor or a motor hav ing one resultant polar line, the polar pitch is three hundred and sixty d egrees,in a four-pole motor one hundred and eighty degrees, the.

The improvements described above may be applied to motors. of various types and may be varied in many ways. We therefore do not restrict ourselves to the specific forms shown and described; but

\Ve claim as our invention and desire to se cure by Letters Patent 1. The combination in an alternating-current-motor device, of an inducing or primary element, comprising coils or sets of coils connected in series and angularly displaced so as to have different axes of magnetization, an

adjustable resistance connected in multiple with one of said coils or sets of coils whereby A eral of such coils may be shunted individuthe magnitude and phase of the current therein may be varied, and a secondary or induced element in inductive relation to the primary coils as set forth.

2. An induction-motor comprising an induced part, a primary member comprising a closedering iron core, a plurality of inducingcoils arranged in recesses in the face of the core, some of such coils being set at an angle to and overlapping the others, and means adapted to short-circuit some of such coils at will. I

An induction-motor comprising an induced part, a plurality of ind ucing-coils in inductive relation to each other, some of such coils being set at an angle to others so as to develop polarization in a different direction, and means substantially as described, whereby said coils are connected in series or partly short-cireuited at will.

4:. Aninduction-motorcomprisingarevolving closed-circuited armature, a field-magnet or induced core having recesses or slots some of which contain main-circuit inducing-coils, some of which contain otherinducing-coils in mutual inductive relation to said first coils, and the remainder of which slots or recesses contain no Winding, and means, substantially as described, for producing a difference of phase of the currents in said inducing-coils.

5. An induction-motor comprising a shortcircuited revolving armature, an inducingcoil in the main circuit, a second coil also in the main circuit at anangle to and in inductive relation to the first, and a switch adapted to wholly or partially short-circuit one of the ind ucing-coils.

6. Aninduction-motorcomprisingarevolving armature, a field-magnet core carrying main-circuit inducing-coils, other inducingcoils disposed upon the same core overlapping the first, and in series therewith, an unwound portion of said core, and means, substantially as described, adapted to short-circuit some of such coils through a resistance.

7. An induction-motor comprising a revolving armature, a closed-ring field-magnetcore carrying main-circuit inducing-coils in recesses in its face, other inducing-coils disposed in recesses upon the same core and in mutual inductive relation to the first, an unwound portion of said core, and means, substantially as described, whereby such coils are connected in series or are part-1y shortcircuited at will.

8. In an induction-motor for alternating currents, an inducing element comprising a ring core having recesses in its face having a portion wound with an exciting coil or coils connected in the main circuit, another portion wound with a secondary coil in inductive relation to the main circuit, and a third portion without any active winding in combination with an induced element comprising coils connected in closed circuit, said coils being situated in inductive relation to the inducing element, and a resistance in circuit with the coils of the induced element and reducing the lag of current therein.

9. In an induction-motor for alternating currents, an inducing element comprising a ring core having recesses in its face with an exciting-coil in the main circuitand with a secondary coil in inductive relation to said exciting-coil and at an angle therewith-and an induced element comprising coils in inductive relation to the coils of the inducing element and connected in closed circuit, such closed circuit being of relatively high resistance, so as to cause the current therein to be substantially in phase with the eleetromotive force.

10. In an altermating-current motor, the combination of relatively-movable inducing and induced elements, the inducing element comprising an iron core, having a portion wound with an exciting coil or coils, another portion wound with a coil which is closed-circuited when the motor is started and a third portion having no windingwhich is active when the motor is started, and an induced element comprising coils connected in a closed circuit so designed that the current and electromotive force therein are maintained approximately in phase with each other.

11. The method of starting an alternatingcurrent motor which consists of passing an alternating current through a primary winding on the inducing member,generating there by a current in a relatively rotatable armature, inducing, by the joint action of said primary winding and arm atu re-windin g,current in a second winding on the inducing member, artificially regulating the phase of the current in the said second winding, and producing rotation of the armature by the joint action of the two windings on the inducing member.

12. The method of operating a singlc-phase alternating-current motor, which consists in generating by the action of a current due to a single-phase alternating electromotive force, a plurality of alternating magnetomotive forces displaced from each other by phaseangles each equal approximately to one-third of a period, and causing by said magnetomotive forces a relative rotation between the inducing and induced members of the motor.

13. The combination in a single-phase alternating-current motor, of an induced member and means for generating by the action of a current due to a single-phase electrometive force, a plurality of alternating magnetomotive forces displaced from each other in space by angles, each equal approximately to one-third of the polar pitch.

In witness whereof we have hereunto set our hands this 19th day of July, 1803.

EDIVIN IV. RICE, .IR. CHARLES I. STEINMETZ.

\Vitncsses:

JOHN W. GIBBONE'I, THORBURN REID. 

